1. Field of the Invention
The present invention relates to a propulsion unit arrangement for a ship, the arrangement including a motor housing in the water, a motor located in the housing, associated control devices as well as a propeller arranged at the motor's shaft.
2. Description of the Related Art
A conventional motor arrangement for a ship comprises a motor arranged within the ship's hull and a propeller arranged on the end of a motor shaft which extends in a watertight manner through the ship's hull. As the propeller rotates it brings water surrounding the ship into motion and thus creates a reaction force which thrusts the ship forwards. The motor can be a directly employed diesel engine or like combustion engine or, favorably, an electric motor to which necessary electric power is supplied by a conventional combustion engine, a gas turbine, a nuclear power plant or the like. The steering of such ships is conventionally arranged so that a pivoting rudder is provided in the propeller's wake, the rudder deflecting the wake and thus creating a lateral force component in relation to the longitudinal direction of the ship.
Other types of so-called propulsion units are also known, wherein the propeller as such can be pivoted for the purpose of steering the ship. This pivoting motion can be accomplished by means of a rather complicated shaft arrangement, or in such a way that the propeller is arranged at the shaft of a motor which, as such, is arranged to be rotatable around a vertical axis. This latter arrangement is called an azimuthing propulsion device. Such a device is described in, for example, the applicant's Finnish Patent No. 76977, which is being marketed by the applicant under the trademark AZIPOD.
Until now all arrangements implemented for ships have the feature in common that the motors per se, as well as other devices and means, are adapted to constitute an essentially integral part of the ship right from the stage of building the ship. Thus, any thorough repair or replacement of the motor can hardly take place unless the ship is docked, after which substantial portions of the ship are dismantled for enabling the replacement to be done. Thus, the only repair job that is somewhat simply and easily accomplished, is usually the task of replacing a damaged propeller, whilst it always will take a long time indeed to perform other, more extensive repairs.
A further disadvantage of motor arrangements which are implemented separately for each ship is that since a motor is being built separately for each ship in any case, the number of motor alternatives tends to increase, and thus full advantage cannot be taken of long serials. The production costs are affected in an unfavorable manner by the complexity of such arrangements and short serials.